Apparatus with automatic respiration monitoring and display

ABSTRACT

A respiratory device is provided with a display showing a respiration signal related to a breathing pattern of a patient. This signal is derived from the difference between a sensed signal indicative of the respiration and airflow generated by the device and a baseline signal. The parameter is adjusted so that the respiration signal is restricted to a predetermined dynamic range. A short term average of the respiration signal (taken over about 0.5 seconds) and a long term average of respiration signals (taken over about 12 seconds) are calculated based on the CPAP measure. These averages are used to monitor the dynamic change in the respiration signal. If a large variation in either average is detected, the baseline is set to a value selected to rapidly reduce the respiration signal to a lower offset.

This application claims priority to U.S. provisional application Ser.No. 60/139,516 filed Jun. 16, 1999.

BACKGROUND OF THE INVENTION

A. Field of Invention

The invention relates to respiratory systems such as Non-InvasivePositive Pressure Ventilation (NIPPV), nasal Continuous Positive AirwayPressure (CPAP) and other similar apparatus, used, for example, in thetreatment of Sleep Disordered Breathing (SDB) or Obstructive Sleep Apnea(OSA). More particularly, this invention pertains to a respiratoryapparatus which uses an automatic baseline tracking technique to monitorand display a patient's respiration, for example during a CPAP titrationsession of a sleep investigation.

B. Description of the Prior Art

CPAP, NIPPV and similar types of respiratory apparatus function tosupply clean breathable gas (usually air, with or without supplementaloxygen) at a prescribed pressure or pressures, synchronously with apatient's respiration. A suitable CPAP apparatus in which the presentinvention may be incorporated is, for example, the Sullivan® V made byResMed Ltd. of North Ryde NSW, Australia.

A respiratory apparatus typically includes a blower, an air filter, amask or other similar patient interface, an air delivery conduitconnecting the blower to the mask, and a microprocessor-based controlunit. The blower generally includes a servo-controlled motor and animpeller and is used to provide a flow of pressurized air to thepatient. The blower may also include a valve for discharging air.Optionally, the apparatus may include a humidifier which can applymoisture to the air supplied through the air delivery conduit. Thecontrol unit is used to control the functions of the blower, and tomonitor clinical functions and other parameters associated withrespiration. These parameters may be used for the diagnosis of sleep andrespiratory disorders. Respiratory disorders such as apnea, snoring, andpartial airflow limitations can be inferred by a clinician from thepatient's respiration, the associated breathing pattern and signals fromother sensors.

A convenient, established way of monitoring respiration during thediagnosis of a sleep disorder consists of analyzing pressurefluctuations obtained from nasal oxygen cannulae inserted into thepatient's nares. This provides an indication of respiration flow. Ifupper-airway irregularities of a significant number are recorded, a CPAPtitration session may be ordered. The goal of a CPAP titration sessionis to determine what level of CPAP treatment is needed to abolish thebulk of the patient's upper-airway irregularities. Throughout thesession the CPAP level (pressure) is manually adjusted to resolve theirregularities. During such a session, respiration may be assessed byinterpreting the mask pressure signal, a complex pressure signalconsisting of the following components: (a) a CPAP component related tothe positive airway pressure induced by the blower and having a very lowfrequency (in the order of 0–0.1 Hz) and high amplitude (in the order of2–30 cm H₂O); (b) a respiration component related to the normalrespiration of the patient and having a relatively low frequency (ofabout 0.01 Hz) and low amplitude, generally not exceeding 10 mm of H₂O;and possibly (c) a component associated with snoring and having a highfrequency in the range of 30–200 Hz and a low amplitude in the order ofa mm of H₂O. For diagnostic purposes, it is desirable to generate anoutput signal indicative of the last two components (b) and (c) toderive the respiration sequence referred to herein as the respirationsignal.

Prior art respiration monitoring systems use high-pass filtering toseparate the desired components from the complex pressure signal. Thistechnique can be unsatisfactory because: (1) if the high-pass filterexcludes low-frequency components of the respiratory signal, it willcompromise the integrity of the monitored signal; (2) it is slow totrack changes in CPAP component, particularly fluctuations due to leakswhich are often known to cause step changes in the pressure signal; and(3) if performed in software, it requires high resolution and extensivesignal processing.

Another known technique for deriving and monitoring a respiration signaluses a DC-coupled response amplifier without high-pass filtering of thecomplex pressure signal. The disadvantage of a DC-coupled technique isthat the CPAP component appears as a DC offset which must be subtractedfrom the complex pressure signal so that the respiration signal does notexceed the dynamic range of the measurement system. During a titrationstudy, each adjustment of the CPAP treatment pressure may demand anadjustment of the DC offset, if the respiration signal is to stay withinthe dynamic range of the monitoring system. Typically a special manualknob is provided for this purpose which allows an operator to eliminatethe DC offset. Hence, using a DC-coupled response amplifier istime-consuming and requires a manual operation of the respiratoryapparatus, additional training, and constant attention by an operator.

If the CPAP component generated by the blower is continuously known bythe respiration monitoring system, an alternate technique would be tosubtract this CPAP component from the complex pressure signal sensed inthe mask, theoretically leaving just the respiration signal. Thistechnique is impractical because leaks may occur, causing the pressurein the mask to deviate significantly from the pressure set for theblower and because the blower may not be in constant communication withthe sensing device and, therefore, the CPAP component may not always bepresent.

OBJECTIVES AND SUMMARY OF THE INVENTION

In consideration of the above, it is an objective of the presentinvention to provide a respiratory apparatus in which a respirationsignal is generated, the signal being automatically adjusted to lie in apredetermined range.

A further objective is to provide a respiratory apparatus capable ofdisplaying a respiration signal to a clinician by calculating a baselinecorrection and automatically adjusting the baseline to track long and/orshort term variations of the respiration signal.

A further objective is to provide a respiratory apparatus whichgenerates a respiration signal indicative of a patient's respirationwithout the need for an operator to compensate manually for pressurevariations produced by the apparatus.

A key advantage of the invention to a clinician performing a sleep studyis that the need for intervention during the operation of the subjectrespiratory apparatus is reduced or eliminated. The present inventionsimplifies respiration monitoring without sacrificing signal integrity.

A further advantage of the subject invention is that it provides arespiratory apparatus which displays a respiration signal as anindication of the upper airway resistance in a patient, the apparatusbeing reliable and easy to use.

Other objectives and advantages of the invention shall become apparentfrom the following description.

Briefly, a respiratory apparatus constructed in accordance with thisinvention includes a blower providing a flow of pressurized air to thepatient, a patient interface (such as a mask receiving air from theblower), a control unit for managing the blower, and a display to show arespiration signal generated by the control unit. The control unitincludes a pressure transducer for sensing the actual instantaneouspressure within the patient interface and for converting this pressureto an electrical pressure signal, and a summer which subtracts abaseline pressure signal from the pressure signal to generate arespiration signal. The baseline signal can be adjusted automatically ormanually. For the automatic adjustment of the baseline signal, long termand short term averages of the respiration signal are calculated. Theseaverages are used to adjust the baseline signal in a manner that insuresthat the respiration signal remains within the predetermined range.Adjusting the baseline pressure signal compensates for changes in therespiration signal caused by the operation of the blower (i.e., the CPAPcomponent) or other factors, such as the development of a sudden leak.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the elements of a respiratory apparatus constructed inaccordance with this invention;

FIG. 2 shows a block diagram for a control unit for the respiratoryapparatus of FIG. 1;

FIG. 3 shows a flow chart illustrating the operation of the respiratoryapparatus of FIGS. 1 and 2; and

FIGS. 4A–4E show time dependent graphs of a respiration signal generatedby the control unit of FIG. 2 for various operating conditions.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, a respiratory apparatus 10 constructed inaccordance with this invention includes a blower 12 adapted to providepressurized air, a flexible conduit 14, a mask 16 and a control unit 18.The control unit 18 is connected to the mask 16 by a flexible pressureline 20 via a pressure port 22. The control unit 18 is also connected toa display 24 and to the blower 12 by respective cables 26 and 28. Theblower 12 may be a CPAP flow generator such as the one marketed underthe name Sullivan®V generator made by ResMed Ltd. of North Ryde, NSW,Australia.

The mask 16 is used to represent generically any suitable patientinterface such as a nasal mask or a full face mask, such as the Mirage®mask made by ResMed, or other similar devices designed to deliver airfrom the generator 12.

The display 24 is designed to indicate graphically the operation of theapparatus 10 and the respiration of the patient, as indicated, forexample, on chart 30. The display 24 may be a chart recorder, a CRT, aPC or a similar device.

Preferably, control unit 18 is programmable and includes a screen 32 andtwo rocker switches 34 and 36. The first rocker switch 34 is marked withup and down arrows, as shown, and is used to select a mode of operationfrom a menu on screen 32. The other switch 36 is marked with + and −symbols and may be used to select and change the values of certainprogrammable parameters associated with the operation of the apparatus10. Finally, an override switch 38 is also provided on control unit 18to override the operation of the apparatus. Control unit 18 monitors theoperation of the blower 12 and generates a signal indicative of therespiration of the patient for display.

The apparatus 10 may be used to perform sleep studies and may beinstalled in a hospital, clinic, or patient's home. For this purpose,the control unit 18 monitors the respiration of the patient through mask16 and configures the blower 12 to provide a controlled pressurized airinto the mask 16 through conduit 14 when required, as is well known inthe art.

As shown in FIG. 2, the control unit 18 includes a microprocessor 40, apressure sensor 42, an analog-to-digital (A/D) converter 44, anamplifier 46 and a summer 48. The pressure sensor 42 is used to detectthe current pressure within the mask 16 and to send a correspondingcurrent pressure signal Pc to the A/D converter 44 and to the summer 48.The microprocessor 40 uses the current pressure Pc in the mask to derivea baseline pressure signal Pb which is summed with signal Pc.

More particularly, the summer 48 subtracts the baseline pressure signalPb from the current pressure Pc. The resulting adjusted pressure Pa(Pa=Pc−Pb) is fed to the amplifier 46 which amplifies it at a gain G(selected by the microprocessor) to generate a respiration signal R.

Referring to FIG. 3, during operation of the apparatus the baselinepressure signal Pb is determined as follows. In step 100, a currentpressure Pc is first determined dynamically by sensor 42. Using thissignal Pc, and a nominator default value Pb0 (selected as discussedbelow), the signal Pa is calculated using formula Pa=Pc−Pb. This signalPa is then amplified at gain G to obtain respiration signal R. In step102 a long term average parameter Pl, which is indicative of a long termaverage of the respiration signal R, is calculated. Parameter Pl may bea moving average of the respiration signal taken over the previous 12seconds.

In step 104, microprocessor 40 determines a short term average parameterPs indicative of a short-term average of the respiration signal R.Parameter Ps may be a moving average of the respiration signal takenover the previous 0.5 seconds. Parameter Ps is effectively indicative ofthe transient pressure noise within the mask.

These calculations are made by the control unit 18 to determine pressurevariations within system 10 attributable to extraneous causes, i.e.,variations caused by factors other than the respiration of the patient.For example, if the blower 12 is a CPAP flow generator, then thepressure variations may be due to the generated CPAP (continuouspositive airway pressure) air flow. The baseline pressure signal Pb istherefore set using these pressure variations, as discussed below.

Next, the microprocessor 40 performs three checks and adjusts thebaseline signal Pb (if necessary) to compensate for extraneous airpressure variations. The first check (step 106) determines the deviationbetween the current baseline signal Pb and the CPAP. This checkcomprises taking the absolute difference between the long term parameterPl and the current baseline pressure signal Pb, and comparing thisabsolute difference to a predetermined threshold pressure Pm. Thisthreshold pressure Pm maybe a fraction (for example, ⅛th) of the outputdynamic range of amplifier 46. If this absolute difference is largerthan Pm, then in step 108 the baseline pressure Pb is set to theparameter Pl.

If no significant deviation between the current signal Pb and CPAP isfound in step 106, (i.e. |P|−Pb|<Pm) then a second check is performed instep 112. Under certain conditions, the CPAP can change rapidly. Thisrapid change may be due, for example, to an abrupt leak in the mask 16,or because the blower 12 is activated and starts pumping air into themask. The purpose of this second check is to insure that the baselinesignal Pb tracks the CPAP during its short-term excursion. Morespecifically, in step 112 a test is performed to determine whether theabsolute difference between the short term average pressure parameter Psand the baseline pressure signal Pb has exceeded a threshold pressure Pifor a period of Ti. The period Ti is defined as the maximum time periodfor which a healthy adult can sustain a continuous inspiration orexpiration. Typically Ti is about 6 seconds and Pi is about 3 cm H₂O.Alternatively, the threshold pressure Pi may also be set as a fractionof the dynamic range of the amplifier.

If in step 112 the absolute difference |Pb−Ps| is determined to begreater than Pi for the last Ti seconds, then in step 114 the baselinepressure Pb is set to the parameter Ps. The process then recycles tostep 100 with the new value for Pb being used instead of Pb0.

The third check is performed in step 116. This step is provided as ameans for a clinician to override the current value of the baselinesignal Pb. For example, when the clinician activates pushbutton 38 (FIG.1), the microprocessor 40 receives an override control signal. If thisoverride signal is sensed, then the baseline pressure signal Pb is setto Ps (step 118). The check for an override signal is shown step 116 asfollowing a ‘NO’ decision in step 112, however, it may be performed atany other time.

When in automatic mode, the control unit operates in accordance with theflow chart of FIG. 3, as described above. However, certain parameters,such as the initial value of the baseline signal Pb and the gain G maybe adjusted by the clinician. For example, baseline signal Pb may be setto a nominal or default level Pb0 in the range of 0–35 cm H₂O usingswitch 36. If no manual override is detected in step 116 then theprocess recycles to step 100.

The effects of adjusting the baseline pressure signal Pb in the mannerdescribed in FIG. 3 are best understood by reference to the waveforms ofFIGS. 4A–E. In each of these figures, the current pressure (Pc) withinthe mask 16 is measured by pressure sensor 42 and processed by thecircuit shown in FIG. 2. The respiration signal R of amplifier 46 isdepicted as a function of time. Conventionally, a higher mask pressure(corresponding to exhalation) is shown as a negative signal(corresponding to a mask pressure) while inhalation is indicated in theFigures (when applicable) as a positive signal. When the respirationsignal reaches the edge of the dynamic range of the amplifier it isclipped, as discussed in more detail below.

FIG. 4A shows the operation of the apparatus 10 when mask 16 is notsecured to a patient and the baseline adjustment feature is disabled. Asindicated in this figure, as signal R increases, it eventually reaches amaximum threshold M defined by the dynamic range of the amplifier 46.The respiration signal R is clipped at level M.

FIG. 4B is similar to FIG. 4A with the exception that the mask 16 hasbeen secured to a patient and the respiration component is present. Whensignal R reaches level M, it is clipped.

FIG. 4C shows the respiration signal R and its long term average Pl whenthe baseline adjustment feature has been activated. As this figuredepicts, prior to t=T1, the long term average Pl is relatively stableand baseline pressure signal Pb is set to its default value Pb0. At t=T1the pressure signal increases rapidly, toward M, and stays at thatlevel. Therefore both Pl and Ps start increasing. As soon as Pl exceedsPb by more than the preselected threshold Pi, the baseline pressure isset to Pl (steps 106, 108). But since Pl increases relatively slowly andsince Pa is very high, initially this change in Pb has no effect. Aftersix seconds in this mode, however, the criteria of step 112 is met, andPb is set to Ps (steps 112, 114). As a result, at t=T2 the respirationsignal R is corrected automatically so that is centered around Pl.

FIG. 4D shows the respiration signal R staying below the threshold levelM but drifting slowly. Therefore, the long term average Pl drifts aswell. When Pl becomes too large, Pb is adjusted as at T3 and T4 causingthe respiration signal R to approach the horizontal axis. In thismanner, the respiration signal R is maintained within the dynamic rangeof the amplifier 46.

FIG. 4E shows a sequence wherein initially at t=T5 there is a rapidchange in the current pressure Pc. This change is handled by the systemin the same manner as described above regarding FIG. 4C. This rapidchange is corrected at t=T6 and is followed by a gradual pressurechange. The gradual pressure change is corrected at t=T7, T8, T9 and T10as shown.

Curves similar to those of FIGS. 4A–4E can be shown on display 24 sothat a patient's breathing and the operation of the baseline adjustmentcircuit of FIG. 2 can be monitored.

At any time, the clinician may activate the override pushbutton 38 whichimmediately sets the baseline pressure signal Pb to the short termaverage Ps, thereby rapidly centering the respiration signal R to themiddle of the effective dynamic range of the system.

In summary, the subject device proffers the following advantages:

-   -   a) It utilizes a DC-coupled amplifier, thereby insuring signal        spectrum that extends to 0 Hz.    -   b) Its automatic baseline adjustment feature can be turned off        at will, leaving the clinician with the standard manual baseline        adjustment.    -   c) Changes in the respiration signal are presented clearly to        the clinician. In one embodiment, automatic adjustments are        indicated by explicit markers corresponding to changes in the        baseline pressure signal.    -   d) Adjustments of the baseline pressure signals are made only to        prevent the respiration signal from moving outside the dynamic        range of the amplifier.    -   e) Adjustments in the baseline pressure signal are preformed        fast enough to track typical automatic or manual-titration        without having the respiration signal R exceed the dynamic range        of its amplifier.    -   f) Tracking does not change as a result of respiratory activity        because it follows CPAP changes only.    -   g) For very rapidly changing CPAP pressures (e.g., during the        start-up period of the blower) where automatic tracking may fail        to keep up, a manual baseline capture is provided to allow        instantaneous baseline adjustments.

The invention has been described in conjunction with a particular typerespiratory apparatus, however it may be incorporated into other kindsof devices as well. For example, in some respiratory devices respirationmonitors are used which include effort sensors such as respiratory bandsor suprastemal notch sensors. These effort sensors infer the effortexpanded by the patient during respiration and generate signals that areshown on a display. Under certain circumstances, for example when thepatient moves or shifts position, the sensor signals undergo a largeshift which exceeds the dynamic range of the display. The presentinvention may be used in such devices to cause the sensor signals toreturn to the dynamic range of the display.

Obviously numerous modifications may be made to this invention withoutdeparting from its scope as defined in the appended claims.

1. A respiratory apparatus for delivering a flow of air to a patientsuffering from sleep disordered breathing comprising: a blower thatgenerates a flow of pressurized air; a patient interface adapted todeliver air from said blower to the patient; a display receiving anddisplaying signals and having a predetermined display range; and acontrol unit coupled to said patient interface and adapted to sense abreathing parameter, said control unit including a display adjustingcircuit means for operating on said breathing parameter to generate arespiration signal indicative of the breathing pattern of the patient;said control unit further including a first averager used to determine along term average of said breathing parameter, and a second averagerused to determine a short term average of said breathing parameter, saiddisplay adjusting circuit means adjusting a base line of said breathingparameter in accordance with at least one of said long term and shortterm averages to restrict said respiration signal to said predetermineddisplay range; and wherein said display receives said respiration signaland presents it within said predetermined range.
 2. The respiratoryapparatus of claim 1 wherein said control unit includes a pressuresensor adapted to detect a pressure signal indicative of a pressurewithin said patient interface, said parameter comprising said pressuresignal.
 3. The respiratory apparatus of claim 1 wherein said controlunit includes a baseline generator generating a baseline signalcorresponding to the baseline of said breathing parameter, saidrespiration signal being related to said breathing parameter and saidbaseline signal.
 4. The respiratory apparatus of claim 3 wherein saidbaseline generator is coupled to said first averager and has codedcontrol instructions to set said baseline signal to a value related tosaid long term average.
 5. The respiratory apparatus of claim 1 whereinthe display adjusting circuit means includes coded control instructions,and wherein in accordance with the coded control instructions saiddisplay adjusting circuit means adjusts said respiration signal in afirst manner dependent on said long term average in one set ofconditions, and adjusts said respiration signal in a second mannerdependent on said short term average in another set of conditions. 6.The apparatus of claim 1 wherein said control unit is further configuredand adapted to control changes in the pressure of the pressurized air.7. A respiratory apparatus used to provide air under controlledconditions to a patient with a pulmonary deficiency, said respiratoryapparatus comprising: a blower that generates a flow of pressurized air;a patient interface that delivers said flow of air to the patient; adisplay for showing signals, said display having a predetermined displayrange; and a control unit coupled to one of said blower and patientinterface to derive a parameter indicative of said flow of air and thebreathing of the patient, said control unit having a signal processingunit that processes said parameter to generate a respiration signalindicative of said breathing and a display adjusting circuit means fordetermining a long-term average value of said parameter and a short-termaverage value of said parameter and for adjusting a baseline value ofsaid parameter in accordance with at least one of said long-term andshort-term average values to restrict said respiration signal to saidpredetermined display range wherein said display shows said respirationsignal within said predetermined range.
 8. The respiratory apparatus ofclaim 7 wherein said display adjusting circuit means is constructed andarranged to adjust said respiration signal in one of a first mannerdependent on said short term average value and a second manner dependenton said long term average value.
 9. The respiratory apparatus of claim 8wherein said display adjusting circuit is adapted to generate a baselinesignal, said baseline signal being subtracted from said parameter togenerate said respiration signal.
 10. The respiratory apparatus of claim9 wherein said display adjusting circuit means is adapted to set saidbaseline signal to a first value when an absolute difference betweensaid baseline signal and said long term average value exceeds a firstthreshold.
 11. The respiratory apparatus of claim 10 wherein saiddisplay adjusting circuit means is adapted to set said baseline signalto a second value when an absolute difference between said baselinesignal and said short term value exceeds a second threshold.
 12. Therespiratory apparatus of claim 11 wherein said first threshold value isrelated to said predetermined range.
 13. The respiratory apparatus ofclaim 11 wherein said second threshold value is related to a pressuresustained by a healthy person during a single continuous sustainedinspiration or expiration.
 14. The respiratory apparatus of claim 7wherein said display adjusting circuit means is constructed and arrangedto adjust said respiration signal when the difference between said shortterm average value and the predetermined threshold exceeds apredetermined threshold value for at least a predetermined duration. 15.The apparatus of claim 7 wherein said control unit is further configuredand adapted to control changes in the pressure of the pressurized air.16. A method for presenting a respiration signal indicative of thepatient's breathing pattern on a display having a predetermined displayrange, the method comprising the steps of: determining a parameterrelated to the breathing of the patient; determining a short termaverage value of said parameter and a long term average value of saidparameter; generating said respiration signal based on said parametersaid respiration signal having a baseline value; adjusting said baselinevalue in accordance with at least one of said long term and short termaverage values to maintain said respiration signal within saidpredetermined display range; and displaying said respiration signal onsaid display.
 17. The method of claim 16 further comprising, taking adifference between said baseline value and said parameter to derive anadjusted signal.
 18. The method of claim 17 further comprisingdetermining an absolute difference between said long term average valueand said baseline value and if said absolute difference is not less thana first threshold, then setting said baseline value to said short termaverage value.
 19. The method of claim 18 wherein said long term averagevalue is calculated over a period longer than a typical breath of aperson.
 20. The method of claim 19 wherein said long term average valueis calculated over a period of about 12 seconds.
 21. The method of claim18 wherein said first threshold is related to said predetermined range.22. The method of claim 21 wherein said first threshold is a fraction ofsaid predetermined range.
 23. The method of claim 18 wherein said longterm average value is taken over a period which is not longer than atypical breath of a person.
 24. The method of claim 17 wherein saidshort term average value is taken over a period which is much shorterthan a typical breath of a person.
 25. The method of claim 24 whereinthe period is about 0.5 sec.
 26. The method of claim 25 wherein saidfirst threshold is related to a minimum pressure maintained by a personduring a single continuous inspiration or expiration.
 27. A method ofkeeping a respiratory signal from a patient within a predetermineddynamic range of an output/display unit comprising the steps of:determining a respiratory parameter indicative of the patient'srespiration; calculating a relatively long term average of therespiratory parameter calculating a relatively short term average of therespiratory parameter; and automatically adjusting a presentation ofsaid respiratory parameter based on at least one of said long term andshort term averages to generate the respiratory parameter within saidpredetermined dynamic range.
 28. The method of claim 27 furthercomprising automatically adjusting said parameter when said parameter isoutside said predetermined range for a predetermined duration.
 29. Themethod of claim 28 wherein said predetermined duration is long comparedwith the duration of a typical patient inspiration.
 30. The method ofclaim 28 wherein said predetermined duration is long compared with theduration of a typical patient expiration.
 31. The method of claim 28wherein said predetermined duration is approximately 6 seconds.
 32. Arespiratory apparatus for displaying a respiration signal indicative ofa patient's breathing pattern during delivery of airway pressuretreatment comprising: a pressure transducer to generate a pressuresignal proportional to pressure in a patient airway treatment interface,wherein the transducer is coupled to the patient airway treatmentinterface; a processor coupled to receive the pressure signal, whereinthe processor includes programmed control instructions, saidinstructions controlling display adjusting steps for restricting apresentation of a respiration signal within a predetermined displayrange in a manner that does not change the pressure of the air deliveredfrom the respiratory apparatus to the patient by generating a baselinesignal from at least one average of the pressure signal; a summercoupled to receive the pressure signal and baseline signal to generatethe respiration signal; an amplifier coupled to the summer; and adisplay screen coupled to the amplifier to present the respirationsignal in the predetermined display range.
 33. The apparatus of claim 32wherein the programmed control instructions further control the step ofgenerating the baseline signal by selecting a particular average from aplurality of averages taken over different averaging periods, whereinthe selecting of the particular average is a function of a set ofconditions.
 34. The apparatus of claim 33 wherein the set of conditionscomprises a threshold comparison of a difference between a currentbaseline signal and one average from the plurality of averages.
 35. Theapparatus of claim 34 wherein the set of conditions further comprises atime period during which the threshold comparison must be satisfied inthe selecting of the particular average.
 36. The apparatus of claim 32further comprising a blower coupled to the processor wherein saidprocessor is configured and adapted to control changes in the pressureof the pressurized air delivered by the blower.
 37. A respiratoryapparatus for delivering a flow of air to a patient suffering from sleepdisordered breathing comprising: a blower that generates a flow ofpressurized air; a patient interface adapted to deliver air from saidblower to the patient; a control unit coupled to said patient interfaceand adapted to sense a parameter characteristic of said flow of air,said control unit including a display adjusting circuit means foroperating on said parameter to generate a signal indicative of thebreathing pattern of the patient; said control unit further including afirst averager used to determine a first average of said signal, saiddisplay adjusting circuit means for restricting said signal within apredetermined display range in response to said first average in amanner that does not change the pressure of the air delivered from theblower to the patient; and a display adapted to show said signal;wherein said first averager is adapted to generate said first averageover a first time period, wherein said control unit further includes asecond averager generating a second average of said signal over a secondtime period which is much shorter than said first time period, andwherein said display adjusting circuit means adjusts said signal in afirst manner dependent on said first average in one set of conditions,and adjusts said signal in a second manner dependent on said secondaverage in another set of conditions.
 38. A method for presenting arespiration signal indicative of the patient's breathing pattern in arespiratory apparatus adapted to provide a flow of pressurized air to apatient the method comprising: determining a parameter within the devicerelated to the flow of pressurized air and the breathing of the patient;adjusting said parameter based on a baseline signal to generate arespiration signal within a predetermined display range based on anaverage value of said respiration signal in a manner that does notchange the respiratory treatment delivered to the patient by taking adifference between said baseline and said parameter to derive anadjusted signal; displaying said adjusted signal; and determining anabsolute difference between said average value and said baseline signaland if said absolute difference is not less than a first threshold, thensetting said baseline signal to said average value.
 39. A method ofdisplaying a respiratory parameter on a display apparatus having adynamic range, the method comprising the steps of: monitoring therespiratory parameter calculating a relatively long term average of therespiratory parameter calculating a relatively short term average of therespiratory parameter; and adjusting a baseline value of the respiratoryparameter in accordance with at least one of the relatively long termaverage and the relatively short term average so as to maintain thedisplay of the respiratory parameter within the dynamic range of thedisplay apparatus.